In general, an optical fiber has a protective coating layer for protecting a glass fiber. Patent Literature 1 describes an optical fiber including a primary coating layer and a secondary coating layer with which a glass fiber is covered. In the literature, the outer radius, the Young's modulus, the linear expansion coefficient and the Poisson's ratio of the primary coating layer are adjusted to thereby allow a void or cracking to occur in the primary coating layer, preventing the transmission loss of the optical fiber.
In addition, Patent Literature 2 describes a colored optical fiber having two coating layers: a primary coating layer and a secondary coating layer; in which any of the primary coating layer and the secondary coating layer is colored in order that both of microbend resistance and hot water resistance are satisfied.